Rocket launchers include shoulder-launched missile weapons, which category encompasses any weapon that fires a rocket-propelled projectile at a target, yet is small enough to be carried by a single person and fired while held on one's shoulder. Specific types of rocket launchers within this group include the rocket-propelled grenade, better known as the RPG, which is a type of shoulder-launched anti-tank weapon; the anti-tank guided missile, a guided missile primarily designed to hit and destroy heavily-armored tanks and other armored fighting vehicles; and the man-portable air-defense systems, which provide shoulder-launched surface-to-air missiles. A smaller variation is the gyrojet, a small arm rocket launcher with ammunition slightly larger than that of a 0.45-caliber pistol. Generally speaking rocket launchers fire projectiles that continue to propel themselves after leaving the barrel of the weapon. In some situations, it may be desirable to guide the aiming of a rocket launcher using a sight, such as a laser sighting device, however many rocket launchers only have traditional iron sights for daylight use.